A known operation apparatus such as a pointing device is operable on a two-dimensional operation surface specified by the Y-axis and the X-axis perpendicular to each other. In such an operation apparatus, when an operation knob is moved on the two-dimensional operation surface, the operation knob may be rotated around the Z-axis, which is perpendicular to the X-axis and the Y-axis. When an operation knob has a simple design such as a circular shaped design in a single color, the user may not visually recognize rotation of the operation knob even when being rotated. Alternatively; when an operation knob is in a rectangle shape or when an operation knob has a surface with a texture, the appearance of the operation knob may be spoiled when rotated. Consequently, design of the operation knob may be spoiled.
For example, Japanese Patent Application 2008-246263, which corresponds to U.S. patent application Ser. No. 12/564,330, discloses an operation apparatus configured to restrain rotation of an operation knob around the Z-axis. Specifically, the operation apparatus includes an X-Y slide mechanism having an X slider configured to parallel shifting of the operation knob in the X-axis direction and a Y slider configured to parallel shifting of the operation knob together with the X slider in the Y-axis direction. Both the X slider and the Y slider of the operation apparatus are configured to guide movement of the operation knob in both the X-axis direction and the Y-axis direction and restrain rotation of the operation knob around the Z-axis. However, in the operation apparatus, an operation feeling may not be satisfying. Specifically, the moving operation of the operation knob is caused by sliding the X-Y slide mechanism in different two directions of the X-axis direction and the Y-axis direction against sliding friction. In particular, an operation feeling may be notedly spoiled when the operation knob is moved in an oblique direction between the X-axis direction and the Y-axis direction. In addition, in such a moving operation in an oblique angle, a play (backlash) may occur when sliding in the X-axis direction and the Y-axis direction is alternately repeated.
Further, it is noted that a known operation apparatus includes a linkage mechanism having link arms including two or more link-connected link arms and an operation knob mounted to the end of the linkage mechanism. In such an operation apparatus, a rotation shaft functions as a movable point. Therefore, play and backlash may be reduced when the operation knob is exerted with a liner sliding motion and moved in the two directions. However, in such an operation apparatus, the operation knob may be easily rotated around the Z-axis. Publication of Japanese Patent Application 2008-173757 (JP-A-2008-173757), which corresponds to U.S. patent application Ser. No. 12/564,430, discloses an operation apparatus provided with such a linkage mechanism. Specifically, the operation apparatus includes a five-joint linkage mechanism for enabling two-dimensional movement of the operation knob and further includes a parallel linkage mechanism to restrict rotation of the operation knob around the Z-axis. Nevertheless, in this case, the number of components increases, and a manufacturing cost also increases.